4 spd auto ?

[ggtsvnv]

Hi all and thanks in advance,

I have an 87 shortbed Silverado with the factory 305 and 700R4. The engine was rebuilt less then 4K ago and runs fine. The question I have is my trans is always shifting back into 3rd gear on even slight grades or if I give my truck more gas on the highway it shifts right down to third. It seems like on slight grades or if I give it just a touch more throtle it ought to stay in 4th (od) not shift to 3rd? Is this normal? Sorry but I'm used to driving a truck with a turbo 350 and the cars I have had in the past (V8 Camaros/Firebirds) did'nt seem to shift as much.

[72 CustomCamper]

That's normal. My dad's 84 did that all the time with the stock 305. Once we went to a 350 it didn't do it as much...


Chuck

[ggtsvnv]

so it sounds like I need to find a way to make a few more horses under the hood. Any suggestions as to easy things to do to make a few more ponies under the hood using my TBI 305 and keeping it smog legal? Would smog legal headers be a good idea?

[72 CustomCamper]

I've been thinking about headers on my 90. I like the shorty's but my truck doesn't have a smog pump. I could go with long tube, but I'd have to weld in an o2 bung...


Chuck

[ggtsvnv]

My concern is that I have never worked on a TBI engine before and I don't want to start making changes that will through the computer out of whack and screw me up smog wise. Dosent someone make a long tube header for these trucks with the O2 sensor fitting already in place ? How will things like a larger throtle body or different intake effect things?

[slugish]

lower gear ratio would cure that . If you are running stock gears in rear - go to a 3.42 or 3.73 with the 700r4.

[kevinr1970]

My '86 GMC long bed 4x4 was doing something similar. 350 w/RV cam, 3.73 axles.
I would be going down the freeway at 65mph and it would just fall out of OD.
ANY GRADE other than flat and it would drop.
My '86 Chev 4x4 diesel did it too. 6.2 diesel, 3.08 axles.

On the GMC long bed I took it to a tranny shop and they did something so the converter locked when in OD. The problem was it would "clunk" into OD and to get it to downshift when needed you would have to put the gas to the floor or manually downshift it.
It sucked to drive. Well, when driving down smaller roads around 45-50mph it drove perfect. But on the freeway it sucked. I hated taking it anywhere.

The funny thing (not HAHA) is that on my '86 GMC 4x4 short bed (305, 3.08 axles), it drives perfect down the freeway. When you want it to downshift you just pushed it down like on any other car and it would downshift.
When I had the owner of the tranny shop test drive it with me in the car he said the lock-up wasn't working so technically it wasn't working right.
But it seems to drive great to me???

[James McClure]

You can "taylor" the 700 to shift a little differently and move the shift points higher. If you know how to adjust the cable the way GM says, just adjust the cable and then hold it securly W\your left hand, push the tab in with your right hand and pull the cable out 1 notch. (about 1\16th") Test drive and if you like it OK, if not move it another notch. Don't go any more than 3 notches. Do this carefully. If you go to far either way control pressures will go nuts and it won't shift at all OR shifts will be late and harsh. jim

[chevymotocross]

I have an 87 as well, 305, 700r4, and AWFUL 3.08 gears. 3.42 or lower are a must in these trucks IMO with such a small engine.

I have done things recently though to help the engine not lug as much. When I bought the truck, it already had true 2.25'' exhaust and k&n filter. I have recently added an injector pod spacer and the CFM-Tech TBI spacer. I highly recommend these upgrades. The injector spacer is cheap and easy to install, and helps low-end and throttle response. The TBI spacer is what really adds noticeable improvements. Throttle response to high end have all been improved greatly. The truck is able to stay in OD a bit longer now on hills before having to downshift.

Before these mods, I would barely use the OD and keep it in D. Kind of sad since OD was one of the big selling points for me with this truck but the 3.08 gears really kill it

[ggtsvnv]

Thanks everyone these sound like some easy ideas to try. the TBI spacer should be easy to fix and I know I have seen them in the summit cagalog. Adjusting the cable is another easy one. When I bought the truck from the orgional owner I thought that the 3:08 posi might be nice for gas miliage but mybe in the not to far future it will get a rebuild with 3:42 gears.